1. Field of the Invention
The present invention relates to a semiconductor device for collecting information about power consumption and controlled to operate on the basis of the information.
2. Description of the Background Art
Semiconductor devices generate heat in accordance with the amount of power consumption. The performance of some circuits is significantly influenced by heat. Such circuits have been designed on the basis of the assumed maximum amount of heat dissipated from the entire device. An example of circuits sensitive to heat includes a DRAM which holds memory contents for a shorter period of time with increasing temperatures and which accordingly must be frequently refreshed with a shorter refresh cycle. Therefore, when the DRAM and another semiconductor device are designed to be integrated together, the maximum amount of heat dissipated from the device must be assumed for determination of the DRAM refresh cycle.
Such assumption is provided for the worst case. Under practical use, the worst situation does not always occur. Then, the above described determination of the refresh cycle is pessimistic (i.e., results in higher levels of specifications than necessary, referred to hereinafter as overspecs). For example, since the DRAM is not permitted to access data and all sense amplifiers operate in unison during a refresh time period, such overspecs unnecessarily deteriorate the performance and lead to unnecessary amounts of power consumption.
One of the common approaches for reducing power consumption is to supply a minimum needed amount of power when no operations are required. This approach may be implemented via software. In a computer, for example, when no programs are currently being executed (in an idle state) and no inputs are entered from a keyboard and a mouse for a given period of time, the operating system of the computer judges that there is no need to subsequently operate for some time to decrease the clock rate of a CPU or the brightness of a monitor.
The above described approach may be readily implemented but is disadvantageous in that all elements of the semiconductor device must be placed into normal operation if only some of the elements are required to operate or permitted to stop. That is, the entire semiconductor device must be idle, failing to minimize power consumption.